EMT here. I have a ton of these kind of stories, but this one sticks out
the best. Warning, NSFW language. This call is from a few years ago:

Our ambulance is dispatched to a residence for a male with leg pain. My
partner and I walk in, and seated in the recliner is an older,
African-American male with a cast on his left leg. He tells us he was in
a motorcycle accident a few weeks ago and broke his leg, and was
discharged from the hospital a couple of nights ago. He says he tripped
over the coffee table and banged his bad leg again really hard, and
wanted to go back to the ER and have them check it out, just to make
sure he didn't re-injure himself.

So after [Boring Medical Terminology Here], we're off to the local
hospital. Talking with him in the back, he seemed like a pretty chill
guy. We're bullshitting back and forth about motorcycles, his ER visit,
his ex-wife, and was just generally an easy going guy.

Half way to the hospital though, he suddenly stops talking, and holds
his hand out to me like he wants to shake my hand. I take his hand and
as I give him a firm handshake, he looks me straight in the eyes and
says the creepiest thing I have ever heard:

"Thank you for everything you are about to do for me."

His eyes then begin to bulge out of his sockets, he starts foaming at
the mouth, and starts screaming at the top of his lungs. "I'M GONNA TAKE
A DIABETIC SHIT ON YOUR DONKEY DICK YOU CRACKER LOVER!" "FUCK ME IN THE
ASS! FUCK ME NOW!" Just over and over again for about a solid 45
seconds, maybe a minute. Then he stops, throws up all over himself, then
collapses on the stretcher, unconscious.

I literally just sat there the entire time in total shock and fear until
he collapsed. Took a breath, checked my pants, told my partner to start
driving faster, then began providing manual respirations to make sure he
kept breathing.

Crazy thing is, I'm talking to one of the ER nurses after we dropped him
off, and she told me the same exact thing happened when he was in there
earlier. And none of the doctors could figure out what it was...